Physical soil properties are analyzed for 29 peat-moorsh soil profiles originated from Kuwasy and Ełk drainage-subirrigation systems located within the Middle Biebrza Basin. Cluster analysis was used to classify these profiles. As the result of the cluster analysis the following two groups of the peat-moorsh soil profiles were distinguished: deep and medium deep with medium and high degree of decomposition (group I) and shallow with medium and high degree of decomposition (group II). For the soil profiles belonging to group I pF measured data were collected and averaged. In order to determine unsaturated hydraulic conductivity "one-step" method was applied. Averaged measured moisture retention and unsaturated hydraulic soil properties were used as parameters in soil water modelling procedure. Hydrological part of SWACROP model was applied to study soil water conditions in peat-moorsh soils. Numerical simulation of water balance of the peat-moorsh soil profile was performed for vegetation period in 1993 using meteorological data recorded at Biebrza meteorological station and field measured groundwater levels as the bottom boundary condition. The following two cases were considered in the simulation procedure: irrigated soil profile located within drainage- subirrigation system and non-irrigated soil profile. As a result of performed numerical simulation it was found that allowable decrease in soil water storage in irrigated soil profile was about 100 mm whereas maximum allowable decrease of groundwater level was estimated as 80 cm. Properly operated subirrigation by controlling ditch water level can assess proper soil moisture content for protection of peat-moorsh soils against mineralization process.
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